Device for generating images and head-up display of automotive vehicle

ABSTRACT

The subject of the invention is a device for generating images ( 10 ) for automotive vehicle head-up display ( 100 ), comprising a liquid crystal screen ( 12 ) and a back-lighting device ( 14 ), said back-lighting device ( 14 ) comprising: at least one light-emitting diode ( 16 ), a housing ( 28; 29 ) surrounding the space lying between the at least one light-emitting diode ( 16 ) and the liquid crystal screen ( 12 ), characterized in that said housing ( 28; 29 ) is bent, the device for generating images ( 10 ) furthermore comprising a reflecting surface ( 31; 32 ) arranged in a bent portion ( 28   c;    29   c ) of the housing ( 28; 29 ) and oriented in such a way as to reflect the light emitted by the at least one light-emitting diode ( 16 ) in the direction of the screen ( 12 ). The invention also relates to a head-up display ( 100 ).

The invention relates to an imaging device for head-up display of a motor vehicle making it possible to inform the users of the vehicle, in particular the driver thereof.

It is known practice to equip a motor vehicle with a head-up viewer, also known as head-up display or HUD. Such a display is placed in the field of view of the motor vehicle driver and displays information concerning the state of the vehicle, of the traffic or the like.

This type of head-up display for a motor vehicle requires an image to be obtained with a brightness that is sufficient for the user, and notably the driver of the vehicle, to be able to see the image sufficiently, and do so in any situation, day or night and according to weather conditions.

Among the possible technologies for forming such an image using the head-up display, the one most commonly used in the prior art is the liquid-crystal screen technology, in particular Thin-Film Transistor Liquid Crystal Display, called TFT-LCD. These TFT-LCD screens require, for the display of an image, a back-lighting generally effected by a plurality of Light-Emitting Diodes (LED). In practice, this TFT-LCD screen and the back-lighting are comprised in an assembly called imaging device, or imager.

Between the liquid crystal screen and the LEDs, the imaging device comprises various light processing and/or filtering elements for optimizing the back-lighting, referred to as a whole as optical system. These elements that are passed through in succession by the light originating from the LEDs toward the liquid crystal screen are generally an array of lenses, a collimator and a diffuser for collimating and homogenizing the light originating from the LEDs.

The collimator is formed by a cylindrical biconvex lens extending transversely over a dimension at least equal to the width of the liquid crystal screen, such as of the order of 30 millimeters, so as to light the liquid crystal screen over the entire width. It is therefore a lens of large size, generally produced specifically.

The imaging device can be installed under the dashboard of the vehicle. However, the space available under the dashboard is reduced. It is in particular occupied by the ventilation duct, the steering column and other components of the vehicle such that it is not always possible to incorporate an imaging device.

One aim of the present invention is to propose an imaging device which is better suited to the space available in the vehicle.

To this end, the subject of the invention is an imaging device for head-up display of a motor vehicle, comprising a liquid crystal screen and a back-lighting device, said back-lighting device comprising:

-   -   at least one light-emitting diode,     -   a housing surrounding the space contained between the at least         one light-emitting diode and the liquid crystal screen,

characterized in that said housing is bent, the imaging device further comprising a reflecting surface arranged in a bent portion of the housing and oriented so as to reflect the light emitted by the at least one light-emitting diode toward the screen.

The use of a bent housing and of a reflecting surface arranged in its bent portion makes it possible to fold the light beam of the back-lighting. The backlighting function of the liquid crystal screen is thus retained while allowing a certain modularity of the imaging device which can have a form better suited to the volume available.

According to a first exemplary embodiment, the reflecting surface is concave. A concave reflecting surface makes it possible to form an additional light collimation stage, making it possible to obtain a beam of parallel light rays at the liquid crystal screen, without requiring the additional use of an additional collimating lens, which is particularly bulky and costly.

The reflecting surface can be defined by the sum of the equation of a cone and of a series of polynomials. The parameters of the equation of the reflecting surface can thus be optimized by software simulation.

According to a second exemplary embodiment, the reflecting surface is an inclined planar surface.

According to one or more features of the imaging device, taken alone or in combination:

-   -   the imaging device comprises a support fixed to the housing, the         reflecting surface being formed by a metallic coating deposited         on the support,     -   the support is obtained by plastic injection,     -   the reflecting surface is formed by an internal surface of the         bent portion of the housing,     -   the reflecting surface is a mirror surface,     -   the bend of the housing forms an angle of between 30 and 120°.

Also a subject of the invention is a head-up display, characterized in that it comprises an imaging device as described previously.

Other aims, features and advantages of the invention will become apparent on reading the following description given in a purely nonlimiting manner and which refers to the attached figures in which:

FIG. 1 is a perspective schematic view of a first exemplary embodiment of an imaging device,

FIG. 2 shows a schematic view of a head-up display,

FIG. 3 is a perspective schematic view of a second exemplary embodiment of an imaging device, and

FIG. 4 is a view of the imaging device of FIG. 3, having pivoted according to a view substantially from below.

In these figures, the identical elements bear the same reference numbers.

Hereinafter in the description, the directions X, Y and Z indicated in FIGS. 1 and 3 by the trihedron (X, Y, Z) set relative to the imaging device 10 will be adopted in a nonlimiting manner.

FIG. 1 represents a first exemplary embodiment of an imaging device 10.

The imaging device 10 comprises a liquid crystal screen 12 and a back-lighting device 14.

The liquid crystal screen 12 is for example a thin-film transistor liquid crystal display, commonly called TFT-LCD screen.

The function of the back-lighting device 14 is to provide the liquid crystal screen 12 with the light needed to form the image. To do this, the back-lighting device 14 notably comprises at least one and preferably a set of light-emitting diodes 16, also called LEDs, and used hereinbelow in the description, placed on a support plate 18 of the back-lighting device 14.

In this embodiment, the support plate 18 comprises a printed circuit board, also called PCB. The printed circuit board used can be for example of FR4 (Flame Resistant) or even IMS (Insulated Metal Substrate) type. The use of an IMS circuit board notably allows a better heat dissipation. The printed circuit board allows both the physical support and the electrical connection (to a power supply and to any other electronic components not represented) of the LEDs 16.

Between the liquid crystal screen 12 and the LEDs 16 there are various light processing and/or filtering elements for optimizing the back-lighting, referred to as a whole as optical system. In the embodiment presented in FIG. 1, these elements forming part of the back-lighting device 14 and passed through in succession by the light originating from the LEDs 16 toward the liquid crystal screen 12 are an array of lenses 20 and a diffuser 22.

The array of lenses 20 makes it possible to form a first stage for collimating the light originating from the LEDs 16 to limit the light power losses if a part of the light is not directed toward the liquid crystal screen 12. Generally, the array of lenses 20 comprises one lens for each LED 16, each lens being arranged above each LED 16.

The diffuser 22, arranged upstream of the liquid crystal screen 12 in the direction of propagation of the light, allows the homogenization of the light, so as to light the liquid crystal screen 12 to allow the formation of an image of good quality, that is to say of substantially uniform brightness. Furthermore, the diffuser 22 makes it possible to mask the interior of the back-lighting device 14.

The back-lighting device 14 also comprises a housing 28 surrounding the space contained between the LEDs 16 and the liquid crystal screen 12, generally called light box, particularly in the motor vehicle field. The housing 28 notably allows the light being propagated from the LEDs 16 to the liquid crystal screen 12 to remain in the back-lighting device 14.

The housing 28 is bent, that is to say that its main orientation is not rectilinear but includes at least one inclination. The bend of the housing 28 forms an angle for example of between 30 and 120°. For example and as represented in FIG. 1, the housing 28 comprises a bend forming an angle of the order of 90°.

The bent portion 28 c of the housing 28 can be inclined in the space according to one or more directions of the reference frame (X, Y, Z), depending on the space available.

The imaging device 10 further comprises a reflecting surface 31 arranged in the bent portion 28 c of the housing 28.

The reflecting surface 31 is oriented so as to reflect the light emitted by the LEDs 16 toward the liquid crystal screen 12.

The use of a bent housing 28 and of a reflecting surface 31 arranged in its bent portion 28 c makes it possible to fold the light beam of the back-lighting. The back-lighting function of the liquid crystal screen 12 is thus retained while allowing a certain modularity of the imaging device 10 which can take a form better suited to the volume available.

The reflecting surface 31 can be a mirror surface which reflects the light rays symmetrically, the angle of incidence of the light rays being equal to the angle of reflection such that all the light rays can be oriented toward the diffuser 22. The coefficient of reflection of the concave mirror surface 31 is for example greater than or equal to 90%.

According to a first exemplary embodiment represented in FIGS. 1 and 2, the reflecting surface 31 is concave.

A concave reflecting surface 31 makes it possible to form a second light collimation stage, making it possible to obtain a beam of parallel light rays at the liquid crystal screen 12, without requiring the additional use of an additional collimating lens, which is particularly bulky and costly.

The concave reflecting surface 31 can exhibit a portion of sphere, of ellipse, of parabola or of hyperbola.

According to an exemplary embodiment, the reflecting surface 31 is defined by the sum of the equation of a cone and of a series of polynomials. This surface can be defined by computer program, such as a “Freeform Surface” obtained by an optical design program like “Zemax”.

The equation of the reflecting surface 31 can thus be defined in the reference frame (X, Y, Z) by the following equation:

$z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\sum\limits_{i = 1}^{N}\; {A_{i}{E_{i}\left( {x,y} \right)}}}}$

in which:

-   -   N is the number of polynomial coefficients,     -   A_(i) is the coefficient of the i^(th) polynomial,     -   c is the curvature which is equal to the inverse of the radius         of curvature R of the cone (c=1/R),     -   r is the root of (x²+y²),     -   k is the conicity (or conic constant), and     -   E_(i) is the term of the polynomial on x and y of degree i.

Depending on the conicity value k, the profile of the reflecting surface 31 will take different forms (k>0: elliptical, k=0: spherical, −1<k<0: elliptical, k=−1: parabolic, k<−1: hyperbolic).

The maximum order of the series of polynomials is twenty for a maximum of 230 polynomial coefficients. The values of the positions x and y are divided by a normalized radius value such that the polynomial coefficients are dimensionless.

The number of polynomial coefficients N can be limited to six, such that the series of polynomials comprises 27 terms: two terms of order one (x, y), three terms of order two (x², xy, y²), four terms of order three (x³, x²y, xy², y³), five terms of order four (x⁴, x³y, x²y², xy³, y⁴), six terms of order five (x⁵, x⁴y, x³y², x²y³, xy⁴, y⁵) and seven terms of order six (x⁶, x⁵y, x⁴y², x³y³, x²y⁴, xy⁵, y⁶).

The parameters of the equation of the reflecting surface 31 can thus be optimized by software simulation.

The housing 28 is for example made of plastic material. It is for example obtained by injection.

Furthermore, the housing 28 can be produced in a reflecting material, such as polycarbonate, to avoid the light power losses by light absorption.

Provision is also made for example for the reflecting surface 31 to be an element distinct from the housing 28, to facilitate production.

The imaging device 10 can comprise a support 26 fixed to the housing 28, for example by gluing or by force fitting, possibly with the interposition of foam. The support 26 is for example made of plastic material. It can be obtained by plastic injection, which makes it possible to obtain any form, including complex forms of “Freeform Surface” type.

The reflecting surface 31 can be formed by a metallic coating, such as aluminum, deposited on the support 26.

FIG. 2 shows the imaging device 10 in a head-up display.

Downstream of the liquid crystal screen 12, the display 100 comprises a planar mirror 126 and a combiner 125. The path of the image is symbolized by three dotted line arrows 30 which, once emitted from the imaging device 10, is reflected on the mirror 126 before being projected onto the combiner 125. The latter allows for an enlargement and/or, by transparency, a display of the image beyond the combiner 125, notably beyond the windshield of the vehicle in a zone 128 or at the level of the windshield of the vehicle equipped with said display 100. The light 30 which is projected onto the combiner 125 is reflected on the eye 127 of the driver of the motor vehicle.

FIGS. 3 and 4 illustrate a second exemplary embodiment of the imaging device 10.

In this embodiment, the optical system comprises a collimator 21 arranged between the liquid crystal screen 12 and the array of lenses 20, making it possible to form a second collimator stage to obtain a beam of parallel light rays, the LEDs 16 being positioned in the focus of the collimator 21.

The collimator 21 is for example a cylindrical biconvex lens, that is to say that the biconvex form of the lens extends by translation in the direction Y, over a dimension at least equal to the width of the liquid crystal screen 12, for example of the order of 30 millimeters, so as to light the entire width of the liquid crystal screen 12.

The reflecting surface 32 is arranged in the bent portion of the housing 29 c, and is oriented so as to reflect the light emitted by the LEDs 16 toward the liquid crystal screen 12.

In this embodiment, the reflecting surface 32 is planar. It forms an angle α greater than 0° and less than 90°, such as an angle of between 30 and 60°, with the main direction P of a light corridor 29 b of the housing 29, situated downstream of the bent portion 29 c in the direction of propagation of the light beam. In the example represented, the reflecting surface 32 is inclined by 45°.

The reflecting surface 32 can be that of an element distinct from the housing 29 or be formed by an internal surface of the bent portion 29 c of the housing 29, making it possible to reduce the number of parts and thus the cost of the imaging device. Furthermore, assembly is simplified. In the example represented, the reflecting surface 32 forms the bent portion 29 c of the housing 29 and links the first light corridor 29 a to the perpendicular second light corridor 29 b.

The liquid crystal screen 12 can be inclined in the imaging device 10. It forms an angle for example of between 0° and 40° with the main direction P of the second light corridor 28 b of the housing 28. The inclined screen 12 makes it possible to avoid the dazzling of the driver by the light rays from the sun by reflection in the mirror 126 of the display 100. 

1. An imaging device for head-up display of a motor vehicle, comprising a liquid crystal screen and a back-lighting device, said back-lighting device comprising: at least one light-emitting diode; a housing surrounding the space contained between the at least one light-emitting diode and the liquid crystal screen, wherein said housing is bent; and a reflecting surface arranged in a bent portion of the housing and oriented to reflect the light emitted by the at least one light-emitting diode toward the screen.
 2. The imaging device as claimed in claim 1, wherein the reflecting surface is concave.
 3. The imaging device as claimed in claim 1, wherein the reflecting surface is defined by the sum of the equation of a cone and of a series of polynomials.
 4. The imaging device as claimed in claim 1, wherein the reflecting surface is an inclined planar surface.
 5. The imaging device as claimed in claim 1, further comprising, a support fixed to the housing, the reflecting surface being formed by a metallic coating deposited on the support.
 6. The imaging device as claimed in claim 5, wherein the support is obtained by plastic injection.
 7. The imaging device as claimed in claim 1, wherein the reflecting surface is formed by an internal surface of the bent portion of the housing.
 8. The imaging device as claimed in claim 1, wherein the reflecting surface is a mirror surface.
 9. The imaging device as claimed in claim 1, wherein the bend of the housing forms an angle of between 30 and 120°.
 10. A head-up display comprising an imaging device as claimed in claim
 1. 